1. Field of the Invention
The present invention relates generally to a fluid dispensing utensil and, more particularly, to a writing instrument having a reservoir between a tip and a capillary storage.
2. General Background and State of the Art
Writing instruments are commonly used to deliver liquids such as ink, paint, adhesive, shoe polish, lotion, medicine, perfume, makeup, Whiteout(copyright) and food. In one type of fluid dispensing utensil, a relatively large volume of fluid is stored in a non-capillary container (or reservoir) where it is allowed to move freely. Pens which incorporate such a container, for example, are referred to as xe2x80x9cfree inkxe2x80x9d pens or markers. U.S. Pat. No. 6,095,707 issued to Kaufmann discloses such a pen. That is, the ink in the reservoir is usually in a liquid state and is free to move about as the writing utensil is moved. One of the nice features of free ink markers is that they are visually appealing to users as the liquid moves around within the container. Moreover, free ink markers tend to last longer than other pens.
Liquid in these utensils is transferred from the container to the delivery end (often referred to as a tip or a nib) via a capillary conveying line or referred to as a capillary wick. A slight vacuum (underpressure) relative to the atmosphere is maintained within the container which prevents liquid in the conveying line from escaping from the utensil until the tip is brought into contact with the surface onto which liquid is to be dispensed. At this point, the force of attraction of the surface and the capillary force of the space between the surface and portions of the tip, which are not in direct contact with the surface, will cause the liquid to flow from the tip to the surface. As liquid is dispensed, air enters the container in a controlled manner via an air inlet that is formed in the container and ends within the liquid. The air replaces the liquid so as to maintain the vacuum at a relatively constant level.
To deal with the problem of leakage caused by air expansion within the container, a capillary storage is used to absorb the excess liquid. Specifically, when the air within the container is heated, it expands. Alternatively, as the writing instrument is used in a higher elevation, the underpressure within the container will rise and increase the vapor pressure on the liquid. This forces excess liquid to flow through the conveying line via capillarity action. To handle the excess liquid, some ink pens or markers include an overflow chamber having a capillary storage that will absorb the excess ink. Fountain pens, for example, include a capillary storage in the front section of the writing instrument next to the tip.
Because the capillary storage is on the front section of the writing instrument or below the reservoir in a writing position, the head pressure of the liquid in the reservoir may keep at least a portion of the capillaries in the capillary storage wet. This means that when there is a rise in temperature or pressure within the reservoir, only the unwetted or dry capillaries in the capillary storage can absorb the excess ink from the reservoir. As such, the capillary storage may need to be oversized to account for the fact that at least some portion of the capillaries will be wetted due to the head pressure in the reservoir. However, a larger capillary storage means that the circumference of the writing instrument, which is housing the capillary storage, needs to be bigger as well. This is one of the reasons why a free ink writing instrument is generally thicker than a ballpoint pen, for example, and therefore not as comfortable for the user to utilize.
Still further, the longer the capillary conveying line, the greater flow resistance it has to convey the ink from the reservoir to the tip. This means that if a user writes quickly or for a long duration of time, the conveying line may dry out and therefore not write properly.
Still further, most free ink writing instruments are assembled from several pieces including a capillary conveying line capillary storage, a divider separating the reservoir and a storage area, all enclosed in a container. All of the above pieces add cost and manufacturing time to manufacture a writing instrument. To minimize the cost of the writing instrument, there is a need to manufacture a writing instrument with fewer pieces. Moreover, there is a need to keep most if not all of the capillaries in a capillary storage dry so that most, if not all, of the capillaries in a capillary storage may absorb excess ink from the reservoir. Even further, there is a need to minimize the flow resistance in the conveying line so that a sufficient amount of ink is delivered to the tip of the writing instrument under most if not all writing conditions.
One of the features of the present invention is to provide a writing instrument having a relatively small circumference so that it may be comfortably held in a user""s hand for writing. Another feature of the present invention is to minimize the flow resistance in a conveying line so that a sufficient amount of ink or liquid may be delivered to a tip of the writing instrument. Still another feature is to provide a writing instrument that is easier to manufacture at a lower cost.
The present invention accomplishes the above features by providing a reservoir for holding liquid or ink between a capillary storage and a tip. That is, according to one embodiment of the present invention, the capillary storage is above the reservoir so that any head pressure in the reservoir or the column of liquid does not affect the capillary storage. This means that the capillary storage will remain substantially dry so that most, if not all, the capillaries in the capillary storage may absorb the excess ink in the reservoir due to a rise in temperature or pressure within the reservoir.
Still another feature of the present invention is to have a conveying line running through the reservoir so that at least a portion of the conveying line along the longitudinal access is in direct contact with the liquid within the reservoir. This means that the liquid in the reservoir may convey to the tip with minimal flow resistance. As such, a sufficient amount of liquid is provided to the tip, even when the writing instrument is used in quick strokes or for a long duration of time.
Yet another embodiment of the present invention is to provide a reservoir between the storage and the tip, but without a conveying line. That is, without the conveying line, the unit costs and the manufacturing costs are substantially reduced. In this embodiment, the reservoir is also below the capillary storage, and they are divided by a porous or a capillary divider wall. Here, the porous divider wall is used to regulate air flow into the reservoir. That is, as the temperature or pressure in the reservoir increases, air will displace the liquid in the largest pore in the porous divider wall to equalize the pressure in the reservoir. With regard to the displaced liquid from the largest pore size in the porous divider wall, such liquid may be temporarily stored in the capillary storage that is in direct contact with the porous divider wall. On the other hand, as the temperature or pressure within the reservoir drops, air will flow back into the reservoir through the largest pore size in the porous divider wall.
In situations where the tip is facing upward or in an inverted position, the porous divider wall may be fully saturated and, if there is a rise in temperature or pressure within the reservoir, the excess ink from the reservoir may be temporarily stored in the capillary storage. Likewise, as with the previous embodiment, since the capillary storage is above the reservoir in a normal writing position, a smaller capillary storage may be used because, under normal conditions, most if not all the capillaries in the capillary storage will be empty of liquid. This is principally due to the fact that the capillary storage which is above the reservoir is not affected by the head pressure due to the column of liquid in the reservoir.